Ancient reptile would be condemned to single sex life by 2085

Published: Wednesday, July 2, 2008, 13:22 [IST]

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London, July 2 : Computer modeling has predicted that rising temperatures will lead to male only offspring in an ancient reptile species known as Tuatara, thus condemning the animal to extinction by 2085.

Often described as 'living fossils', the tuatara is a cold-climate reptile that can reach nearly a metre in length.

According to a report in Nature News, researchers studying tuatara, which is the ancient relative of which once roamed the world alongside dinosaurs more than 200 million years ago, made their doomsday prediction using digital terrain maps detailing the consequences for the reptiles' nesting sites of a 4 degree Celsius hike in average temperature.

The entire tuatara population is now effectively trapped on about 30 small islands in New Zealand's north, having been wiped out elsewhere by predators.

They therefore have no chance of adapting by fleeing to cooler climes, according to the researchers.

"Since the mid 1990s, people have been talking about the vulnerability of reptiles to climate change because they have temperature-dependent sex determination. But no one has been able to model it in this type of complexity before," said research leader Nicola Mitchell of the University of Western Australia in Perth.

With the aid of computer software, the researchers combined the physics of heat transfer with terrain data for the four-hectare North Brother Island in New Zealand's Cook Strait.

Using the exact coordinates of 52 known nesting sites of the rarest species of tuatara, along with a database of current soil properties and their constant temperature equivalent, the researchers simulated climate change and then monitored its effect on specific points across the island.

They found that based on maximum warming predictions, the tuatara, which hatch as males when nest temperature during development moves above 21.5 degree Celsius, will be incapable of producing females.

While some argue that this type of model can make unnecessarily sweeping assumptions, Mitchell's colleague Michael Kearney at the University of Melbourne in Australia said that the data were road-tested to predict the soil temperature and sex ratios of natural nests where the researchers already knew the results.

"We asked the model what the ultimate sex ratio would be on nests where we knew the observed temperature fluctuations and it was very consistent with what we had observed," said Kearney.

According to Raymond Huey, a biologist at the University of Washington in Seattle, "Relative to the past, tuatara now have few places to hide, if anything their genetic inertia is now elevated. Moreover, they face a rate of temperature change that is unprecedented over the last 50 million years."